This invention relates to a latch needle for a textile machine. The latch needle has a needle latch which is accommodated in a sawslot of the needle shank and which is pivotally supported by a pivot pin passing through a bearing bore provided in the latch shank.
Latch needles of the above-outlined type are used in a number of textile machines, preponderantly in knitting machines but they may also find application, for example, in special sewing machines. The bearing for the latch has to comply with strict requirements as concerns mechanical stresses as well as the accuracy of the latch guidance. The latch is particularly highly stressed (loaded) if in rapid knitting machines soiled natural fiber yarns, for example, open-end yarns or elastomers are to be processed.
The latch bearing may be structured in different ways. Thus, from European Patent 0 232 466 it is known to have the latch supported by a pin passing through the bearing bore of the latch. The pin is supported in bores provided in the needle shank cheeks that define the sawslot. In the bores fixing elements are positioned that serve as axial abutments for the pivot pin.
Further, latch needles are known wherein the latch is pivotally supported on two bearing pins pressed out of the material of the needle shank cheeks. Such an arrangement is disclosed in U.S. Pat. No. 3,934,109 and U.K. Patent No. 836,297.
Further, German Offenlegungsschrift (application published without examination) 35 46 037 discloses an arrangement where only one of the needle shank cheeks is provided with a bore into which a pivot pin is press-fitted. The pivot pin has a length of approximately two-thirds of the needle shank thickness and engages the opposite needle shank cheek.
All the above-outlined latch supports seek to avoid a premature breakage of the needle shank cheeks, while the latch itself is not given primary consideration. The bearing bore provided in the latch is disposed transversely "centrally" in the latch shank in such a manner that the distances between the edge of the bearing bore and the upper and lower sides of the latch shank are approximately the same. Stated differently: the spacing of the bearing bore from the upper side of the latch shank is the same as from the lower side of the latch shank.
These solutions do not address another problem involved with latch needles: because of frictional wear and particularly impact-caused wear upon hard collision of the latch with the needle shank as the latch assumes its rearward position, the resulting lever action may cause a breakage of the latch shank in the zone of the bearing bore, thus limiting the service life of the latch needle.